(1) Field of the Invention
The present invention relates to a method and compositions for increasing ectomycorrhizal colonization of the roots of trees, such as conifers and other cultivated trees. In particular, the present invention relates to the use of formononetin, an alkali metal formononetinate or mixtures thereof to increase the colonization.
(2) Description of the Related Art
Throughout the western United States, Ponderosa pine and Douglas-fir trees are planted extensively on a variety of sites in urban, suburban, and forestry environments. Disturbed, compacted soils and hot, dry sites are commonly encountered. First-year mortality of planted trees can be high under such harsh conditions (Amaranthus and Malajczuk 2001; Amaranthus and Perry 1987; Preest 1977; Peterson and Newton 1985; Steinfeld et al. in press) and foresters, landscapers and arborists are always interested in cultural practices at the nursery which may improve tree survival, nutrition and performance.
Mycorrhizal fungal hyphae associate with plant roots in a symbiotic non-parasitic relationship. Two categories of mycorrhizal fungi are vesicular-arbuscular (VAM) mycorrhiza where the hyphae enter the root and penetrate the root cells where they form branched arbuscles. VAM fungi are also referred to as arbuscular mycorrhizas, because not all form vesicles. A second category of mycorrhizal fungi are the ectomycorrhizal fungi. The ectomycorrhizal fungal hyphae associate with the surface of roots of the tree and grow in spaces between the root cells thereby forming a Hartig net around the cells, but do not penetrate the root cells as in the case of the vesicular-arbuscular mycorrhizal fungi. Many tree species will form only one type of mycorrhizal relationship. Yews form VAM relationships, while trees such as firs, pines, spruce, oak, birch, and beech form ectomycorrhizal relationships.
Conifer tree establishment depends on rapid root development and ectomycorrhizal colonization (Amaranthus and Perry 1989). Out-planting performance of inoculated seedlings has been improved in numerous studies by inoculation with ectomycorrhizae (Theodorou and Bowen 1970; Theodorou 1971; Momoh 1976; Ekwebelam and Odeyinde 1985, Amaranthus and Perry 1989). The importance of Rhizopogon sp. ectomycorrhizae in conifer establishment is shown by Castellano (1996) in his review of inoculation success with numerous ectomycorrhizal fungi used in forestry. Nutrient acquisition is considered a major factor in improving seedling performance. Significant increases in phosphorus uptake have been reported for mycorrhiza-inoculated conifer seedlings (Theodorou and Bowen 1970; Lamb and Richards 1971, 1974; Skinner and Bowen 1974a, 1974b; Chu-Chou and Grace 1985). Potassium (Theodorou and Bowen 1970; Lamb Richards 1971), sodium (Melin et al 1958), total nitrogen (Chu-Chou and Grace 1985), and ammonia forms of nitrogen (Finlay et al. 1988) are all increased by mycorrhizal inoculation. Ectomycorrhizae also enhance water uptake by their hosts (Trappe and Fogel 1977; Reid 1979; Parke et al. 1983) although tolerance to low water potentials vary widely among mycorrhizal species (Mahal and Reid 1973; Theodorou 1978; Parke et al. 1983).
The requirements for mycorrhizal sporulation, growth, and formation are still poorly understood despite the importance of the plant and mycorrhizal relationship. Mycorrhizal spores require germination, hyphal growth and root penetration to successfully form mycorrhizae and numerous physical, genetic and chemical factors may be involved. Numerous authors have reported that the presence of living roots are critical for spore germination and hyphal elongation (Siqueira et al. 1985; Bonfante-fasolo 1988; Becard and Piche, 1989). Plant signal molecules produced by roots may be essential for the symbiotic relationship to develop (Siqueira et al. 1991; Nair et al. 1991; Elias and Safir 1987; Graham 1982). The isoflavonoid formononetin (7-hydroxy, 4′-methoxy isoflavone) has been identified as an arbuscular mycorrhizal stimulating factor, promoting hyphal growth and root colonization (Nair et al. 1991, Gianinazzi-Pearson et al. 1989). No information is currently available on the effects of these isoflavonoids on ectomycorrhizal growth and mycorrhizal formation.
U.S. Pat. No. 4,550,527 to Hall et al. describes a carrier material having an adherent layer comprising an inoculum of a mycorrhizal fungus. Hall et al. does not describe using formononetin or alkali metal formononetinate compounds to stimulate the ectomycorrhizal colonization of the roots.
U.S. Pat. Nos. 5,002,603, 5,085,682 and 5,125,955 to Safir et al. describe the use of isoflavones as stimulants for the growth of vesicular-arbuscular mycorrhizal fungi. While Safir et al. describe the use of isoflavones as stimulants for the growth of VAM fungi, there is no disclosure regarding using formononetin and alkali metal formononetinate compounds to stimulate ectomycorrhizal colonization of roots in trees such as firs, pines, spruce, oak, birch, beech and others which harbor ectomycorrhizal fungal species.
U.S. Pat. No. 5,178,642 to Janerette describes ectomycorrhizal fungal inoculants for either woody or herbaceous plants. Janerette does not describe using formononetin or alkali metal formononetinate compounds to stimulate the ectomycorrhizal colonization of the roots.
U.S. Pat. No. 5,691,275 to Nair et al. describes formononetin and alkali metal formononetinate compounds for stimulating, the growth of vesicular-arbuscular mycorrhizal fungi which colonize plants such as corn, soybean, sorghum, asparagus, leek, onion, Taxus sp. and other woody species, coffee, clover, citrus, sea oats, wheat, potatoes and other crop plants. While Nair et al. describes VAM fungi stimulation in certain woody species such as Taxus sp. (Yew) which harbor VAM fungi, there is no disclosure regarding using formononetin and alkali metal formononetinate compounds to stimulate ectomycorrhizal colonization of roots in trees such as firs, pines, spruce, oak, birch, beech and others which harbor ectomycorrhizal fungal species.
While the related art teach compounds for stimulating the growth of vesicular-arbuscular mycorrhizal fungi, there still exists a need for improving ectomycorrhizal colonization of tree roots which harbor these fungal species.